A buffer tube, such as those for a collapsible buttstock on a rifle (such as the M4), is typically a hollow tube that is closed (or partially closed) at one end, wherein the open end is attached to a receiver coupled to a firearm. A buffer tube serves two general functions: first, it holds the recoil spring and a recoil buffer inside its hollow chamber. The recoil spring and recoil buffer push the firearm bolt forward when the trigger is pulled or the bolt catch is depressed. Additionally, the buffer tube acts as an attachment mount for the firearm's collapsible or non-collapsible buttstock.
Conventional buffer tubes are designed in an axially fixed arrangement intended for “normal” use. That is, when firing, the buttstock properly sets on the user's shoulder when the firearm is held orthogonally to the user's body, with the bottom of the firearm pointing straight down toward the ground. However, when a firearm user is under cover, the firearm must often be held at non-orthogonal and non-ideal angles. For example, when the user is on his stomach in a prone position, the firearm may be held somewhat parallel to the user's body, but at a 45° angle relative to the ground because the ammunition magazine is obstructed by the ground. As a result, the firearm is not in a proper shoulder location.
When the buttstock of the firearm is not positioned in the proper shoulder location, shots are inaccurate due to lack of firearm stability. Further, significant recoil drift exists, thus making several shots in quick succession impractical. Finally, recoil may possibly injure the user. Each of which are undesirable. Several other scenarios exist that force a firearm user with a buttstock configured for normal operation to use an improper shoulder location for the buttstock, such as when firing under a vehicle, firing inside of a vehicle, and firing around a corner. Moreover, some firearms are equipped with two or more scopes (or colored dots) that are set for precision shots at different distances. Only one such scope can be set in one line of sight; in order to use multiple sights, these would be attached to the firearm at different lines of sight offset from the normal line of sight (different firearm axial angles), usually set at 45° from the neutral line of sight. In order to use such different scopes, the firearm should be tilted to allow the operator to line up the scope with the line of sight and take aim at a target, however, this will position the firearm buttstock in a non-ideal position for the operator to take a precision shot or control the firearm recoil. A series of quick, proper shots may be what separates a soldier from life or death in these scenarios and having proper shoulder location is critical towards successful, quick shots.
Historically, changing the axial angle of conventional, collapsible buttstocks relative to the rest of the firearm requires disassembling the components of the firearm and then re-assembling them in a desired configuration. As expected, such an approach is impractical for field use and inconvenient, at best, for enthusiast use. For example, U.S. Pat. No. 7,024,812 by James B. Nelson (“Nelson”) discloses a gun stock pivot. More specifically, Nelson describes an accessory that permits the buttstock to rotate to indexed positions about an axis substantially parallel to the axis of the barrel. However, according to the Nelson design, it would be more difficult to quickly and easily switch between positions as Nelson uses locking dowel pins to secure the buttstock in a desired position. Therefore, it is desirable to create a firearm that is capable of changing its buttstock angle quickly, such that it can be properly shouldered when the firearm is not at the standard orthogonal angle relative to its user. More importantly, it is critical to be able to change the buttstock angle while maintaining the target or the potential source of danger in sight.